How does a journalist who has never written a book before and was previously best known for his features in The Palm Beach Post end up finishing a bestselling biography series of the most commanding British statesman of modern times? Ask Paul Reid. He wrote the lion’s share of The Last Lion: Winston Spencer Churchill: Defender of the Realm, 1940-1965, after William Manchester, the author who started the book, passed away. The third and final volume of the biography of Sir Winston S. Churchill begins shortly after he was elected prime minister and guides readers through the war and its aftermath, up until his death in 1965.

Winner of a National Humanities Medal, author and longtime journalist Manchester (1922-2004) published historical biographies such as The Death of a President (on the assassination of JFK),A World Lit Only by Fire (a history of the Middle Ages), American Caesar (a biography of American military general Douglas MacArthur), and his first two biographies of Churchill before he started work on Defender of the Realm in 1988. He wrote up until 1998, when he suffered two debilitating strokes that impaired his speech and partially paralyzed his left leg. He could talk, but he could not write.

So one October evening in 2003, he asked Paul Reid, a close friend and award-winning features writer and food critic for The Palm Beach Post, to complete the book. Manchester and Reid first met in 1998 at Manchester’s Middletown, Conn., home while Reid was reporting a feature about Manchester’s fellow Marines, who were visiting the biographer to lift his spirits.

Reid was well-suited for the mammoth project. He had read an enormous amount about the former prime minister; growing up, he listened to Churchill’s speeches on the family’s RCA Victrola as his father, a United States Naval Academy graduate, flipped pancakes. Manchester specifically did not want a historian to finish his book, but a storyteller who could narrate and create a sense of drama — because, as Reid points out, “we all know how the war ended.” Manchester vowed to stand by and edit — “My red pencils are sharpened,” he told Reid — but he died before he could touch the younger writer’s first stab at a section on the Battle of Britain. Reid was left to sort through his friend’s “clumps,” or book notes, and incorporate British government documents that had been released after Manchester’s death.

Many know Churchill as the steadfast prime minister who led Britain through World War II, but Manchester’s and Reid’s tome shows he was also a bundle of contradictions. He could sit through meetings with The Big Three, but could not sit through Citizen Kane and Oliver Twist because he thought they were too boring. Though English mystery novelist Margery Allingham dubbed Churchill “an unchanging bulldog” and the “epitome of British aggressiveness,” his compassionate side emerged when he spent time with “wollygogs” — his nickname for children — and animals, once asking an adviser what was being done to protect zoo animals from German bombings during the London Blitz. Some days he would walk onto the airfield in velvet slippers and a green-and-red-and-gold dragon dressing gown, while other days he would simply don his birthday suit. And considering Britain faced Nazi Germany alone between 1940-1941, perhaps one cannot blame Churchill for smoking about a dozen cigars a day and drinking morning, noon and night.

TIME talked to Reid about Churchill’s quirks, Manchester’s writing process and finishing a book more than 20 years in the making.

The Last Lion starts off with colorful details about Churchill’s style — such as his habit of sitting in bed, wearing a pink robe, and drinking a bottle of wine for breakfast.

The preamble is meant to introduce Churchill to people who may not have met him before. It was meant to give you a skim coat of his character so that when you find him in the story, laying in bed with a bottle of wine, you’re not surprised. You don’t want to meet the character yelling at a young typist and not know if that’s abnormal behavior. And wow, what a character.

You write that Gone with the Wind was one of Churchill’s favorite films — and also one of Adolf Hitler’s. So that’s one thing they had in common?

They also had in common a hatred of whistling. Churchill banned whistling in the government building. One day, with his bodyguard, he was walking through Whitehall toward Parliament. A little boy was whistling, and Churchill went out of his way to cross the street and yell at him, “Stop that!” And the little boy answered back (I’m paraphrasing wildly), “Who are you old man?” Churchill harrumphed, and the little boy went off and probably started whistling again. But Churchill hated whistling, and he hated cowbells. And telephones ringing. And clocks ticking. And anything that would upset his equilibrium.

But somehow, all the drinking didn’t throw him off.

Well, he had a miracle metabolism. He was who he was. Anyone who tried to drink like that would be in big trouble. I put the drinking out there, but I’m careful to say he could do it without any effect, and Eleanor Roosevelt recognized that. Yet even after he had a few brandies, you didn’t want to have an argument with the guy or discuss tactics.

And then there was that time President Franklin D. Roosevelt wandered in while Churchill was naked.

Churchill was all soldier. He didn’t look it as a round, balding fellow of 65 pushing 70, but he was once a young, dashing soldier. Out in the field, there’s no modesty. So he thought nothing of walking naked out of his bathroom and calling out to a private secretary, “Bring me the latest report!” It didn’t matter who was in the room or the hallway. I’m sure a lot of people walked in on him lots of times when he was stark naked. Didn’t bother him. Didn’t bother Roosevelt either.

Churchill also did not know who Frank Sinatra was. When the singer ran up to him and shook his hand, Churchill asked his private secretary, “Who the hell was that?”

There’s a lot to that scene. First, Churchill simply didn’t like to be touched, except maybe his wife would put her hand on his. Second, this stranger is the most famous singer in the world, and Churchill doesn’t know it. He was not narcissistic, but he was inward-looking, and his doctor and other sources say the same thing. He didn’t really care what you think and didn’t care at all what you feel, even up to and including his own family. In that one little scene, you’ve got his aversion to being touched and his self-centered worldview: there’s Winston Churchill, and then there’s everybody else — including this world-famous singer, and he doesn’t even know who he is. And more importantly, he doesn’t even care.

But he also read everything: the complete Shakespeare, the Bible — for nuance in his speechifying — historians, the ancient Greeks, medieval philosophers, scientific studies, psychology books, geopolitical analysis, newspapers, novelists, like the Hornblower novels, which we would call beach-reading now. So yes, he had these funny quirks, but meanwhile, he’s reading everything — and singing Gilbert and Sullivan all the time that he’s reading.

How did you react when William Manchester asked you to finish writing The Last Lion?

I’ve told people I was flabbergasted, which is true. It was late in the evening, and I remember stepping out to his deck and thinking, “What the heck? Where am I going here?” And the next morning, I woke up and thought, “I better go verify this.” So I was surprised. I never saw it coming. We had been friends for five years, and I had been encouraging him to find someone.

Is there a clear place where Manchester’s writing ended and your writing began?

The short answer is no. It’s almost become a parlor game out there. People are wondering, “Who wrote this line?” In brief, he wrote about 100 pages — typed book pages — between pages 1 and 200. There might be eight or ten in a row, and then I might have added my own perspective and taken the story somewhere else, so there’s not a linear 100 pages of William Manchester. Even the pages he did might have been edited and synthesized.

What are clumps? And how did you use them to write?

Imagine taking two 50-page 8½” x 11″ tablets and Scotch-taping them together in the middle, so now you’ve got an 8½” x 21″ tablet with 100 pages. He created these — cutting, pasting, and taping them together himself. And onto each piece he would [paste] maybe a speech excerpt or a telegram excerpt or part of [French general Charles] DeGaulle’s memoirs. And he had more than 50 of these — about 5,000 pages. They weren’t strictly chronological either, and you couldn’t search them as you can search a Microsoft Word document. They were Bill’s creation, and they spoke to him, but they couldn’t speak to me.

Was there ever a point when you thought you couldn’t finish the book?

No, there wasn’t. In the beginning, I was enough of a blockheaded Bostonian of Scots-Irish descent to go home that weekend and think, “I can do this.” About three years into it, I realized, “I have to do this.”

If I had sat down and seen 2,000 blank typewritten pages typed up, I might have had second thoughts. So I compartmentalized it, and I wrote a scene at a time, which might have grown into a 4-6 page feature story, then I’d have to connect that to the previous scene and transition to the next scene — while keeping in mind this complex cast of characters and battles and simultaneous events happening all over the world.

As you were writing, did you end up differing with Manchester about any particular aspect of Churchill’s life?

First, I found that Churchill drank a lot more than William Manchester had him drinking in the first two volumes. Second, Churchill likely did not suffer from lifelong adult depression. I spoke to several psychiatrists who walked me through the Mayo Clinic symptoms for diagnosing major depression, melancholy, manic depression. I gave them the behaviors of this blind, control patient. In other words, I didn’t say we were talking about Churchill at first. And the psychiatrists said, “You know, occasionally this patient has one symptom, sometimes two, but you’ve got to have several of these 13-15 symptoms active a couple of times a year, including inconsolableness, inability to work, and feeling unloved.” And Churchill never exhibited those symptoms. He drank too much, and he exhibited some of the symptoms some of the time, but I finally concluded he wasn’t a lifelong depressive.

What do you want people to remember about Churchill from reading this book?

He saved Western civilization. I like my Plato, Aristotle, Schopenhauer, Schubert and Einstein, and the whole legacy of the Renaissance in the classical time would have been bulldozed by the Nazis. And that’s what Churchill fought for. Freedom.